The subject matter disclosed herein generally relates to power converters, and more particularly to AC-DC power converters for electrical systems such as in aircraft.
Vehicles, such as aircraft, commonly carry AC generators to generate AC power during flight for powering electrical devices carried by the aircraft. The AC power is typically converted to DC power by a power converter, which provides DC power by applying positive and negative voltages at DC output terminals of the converter relative to a reference voltage. In high power systems the AC power is provided by a polyphase AC source with two or more phase groups, such as a 6-phase AC power source, each phase group having a neutral phase and each neutral phase having a voltage that is different from the voltage of the other. Since the neutral phases have different voltages the reference voltage available from the power converter is uncommitted, and is typically allowed to float relative to the voltages at the neutral phases of the phase groups.
While generally advantageous in terms of efficiency, the uncommitted reference voltage can be load dependent. Further, both the generator and conductors connecting the generator to the converter must be sized for the 6-pulse non-linear current of the converter rectifier—which can require that the generator and converter be more massive than would be required. And in some 6-phase generators the voltage difference between the neutral phase of the generator phase groups can also be imbalanced due to the generator winding end turns, driving DC imbalance currents in the converter transformers, adding weight to the converter.
Such converters and power systems employing such converters have generally been considered satisfactory for their intended purpose. However, there remains a need for improved AC-DC converters, electrical systems employing such converters, and methods of converting AC power to DC power. The present disclosure provides a solution to this need.